1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method for polishing a substrate, such as a wafer, in which devices are formed, and in particular, relates to a multistage polishing apparatus and a multistage polishing method for polishing a flat surface and a peripheral portion of the substrate.
2. Description of the Related Art
In fabricating processes of semiconductor devices, a surface and a peripheral portion (which is also called a bevel portion or an edge portion) of a wafer are polished in order to remove an unnecessary material film. This wafer polishing process is generally divided into a process of polishing the flat surface of the wafer and a process of polishing the peripheral portion of the wafer. The polishing of the flat surface of the wafer is performed by placing the surface of the wafer in sliding contact with a polishing tool, such as a polishing pad, while supplying a polishing liquid (slurry) onto the polishing tool. Such polishing with use of the slurry is called Chemical Mechanical Polishing (CMP). The polishing of the peripheral portion of the wafer is performed by placing a polishing tape in sliding contact with the peripheral portion of the wafer while supplying a polishing liquid (typically pure water) onto the wafer.
As disclosed in Japanese patent publication No. 4655369, Japanese laid-open patent publication No. 2010-141218, and Japanese laid-open patent publication No. 2008-42220, several multistage polishing methods for polishing the flat surface of the wafer and further polishing the peripheral portion of the wafer are proposed. However, in such multistage polishing methods, polishing debris produced in a previous polishing process and/or slurry may adversely influence a subsequent polishing process. For example, the polishing debris may cause scratches on the wafer.